Service engine light intermitant

[steve99]

Okay, here's a strange one. My service engine light doesn't always come on when I turn the key. I believe its supposed to come on when you turn the key and go off when the engine kicks over, unless something is wrong of course. For example today I started it and it came on normally but a few hours later I started it and noticed it didn't come on. This almost made the truck fail inspection. Any ideas on what's going on?

 

thanks

[AZ-Z71]

My 99 does the same thing.